Yeah I made the other thread which kicked up some conspiracys about valve altering their statistics. After making a few posts on the steam forums I got a reply from a Moderator and a Valve employee which pretty much explains everything.

Killah Instinct (Steam forums Moderator) :

QUOTE: "It's very hard to get an accurate number through any stats-page, this has to do with different methods, master servers and the various dimensions the data floats in.

Am sure they Steam: Game page is accurate in it's own way, also note it doesn't really tell when those numbers where recorded - same applies to GameSpy (I doubt they are 'live').

For 3rd party mods, just look here (HL2) or here (HL1)."

There "here's" where hyper links to these websites
HL1: http://www.amxmodx.org/newstats.php
HL2: http://sourcemod.net/newstats.php

*note over 100,000 players playing on AMX servers alone ;)*

Jmccaskey (Valve employee) :

QUOTE: "The new stats on our page are based on users who are connected to Steam and what games they report to be playing via Steam.

The stats at other places like GameSpy are based on querying our master servers which simply report whatever games servers have told them. These numbers can be incorrect in several ways. First, game servers sometimes misreport player stats in an attempt to lure players onto their server even though its actually empty. Second, they can be higher at times due to players who are not connected to Steam playing on VAC insecure servers. Third, the third party sites using the master server data sometimes misreport it because of problems like not including TF2 "custom" servers (and the players on them) in their numbers since they have not updated to support our recent changes to the master server protocol to split servers into standard and custom buckets."

So basicly steam stats only take the data from people playing cs over steam and not from the actual game itself. People who play cs with a crack/don't use steam to play CS are not included in steam statistics (therefore actually hurting our representation)